Many electronic components use integrated circuits or chips. An IC is comprised of semiconductor devices (e.g. diode, transistor etc.) and passive components (e.g., transistors, capacitors, resistors, etc.) that are formed in the surface of a thin substrate of semiconductor material.
One IC can be connected to another IC or other wafer through wafer to wafer bonds. Wafer to wafer bonds relates to joining major surfaces of the wafers. The joined areas of the wafers creates the hermetic seal(s).
One type of wafer to wafer bond relies on a copper pad disposed on each wafer. The copper pad is higher than the surrounding plane of the wafer. A copper pad on one wafer is aligned with the copper pad on the other wafer. Thermo-compression diffusion bonding can be employed to join the copper pads located on each wafer. The ICs are then sealed together with a copper seal ring or a race track near the outer edges of the individual chips. Copper is not biostable and may not provide an adequate seal in vivo for implantable medical devices. Additionally, copper pads that are coplanar with a thermal oxide can be difficult to planarize and polish. For example, copper and thermal oxide can have different polishing rates. It is therefore desirable to develop new techniques for efficiently and hermetically sealing the electronic circuitry in IMDs.